FishnfellaS, when you say hellgrammites, do you mean dragonfly larva? I've heard some bait fishermen call dragonfly nymphs and stonefly nymphs hellgrammites. I can rule out stonefly nymphs in a lake. A true hellgrammite is a dobsonfly nymph which is found only back east.

Crane Prairie Lake in central Oregon also was famous for the number of giant dragonfly nymphs that have almost disappeared in the last few years. There they blame it on over-harvest as people use to collect them and sell them to bait shops